Process for the preparation of aromatic diisocyanates

Abstract

A continuous process for the preparation of aromatic diisocyanates by phosgenation of the corresponding diamines, in which the reaction is carried out in the gas phase. The mean contact time for the gaseous reactants is from 0.5 to 5 seconds with a mean deviation of no more than 6%. The product diisocyanate is obtained in yields of over 95%.

What is claimed is: 
     
       1. A process for the production of an aromatic diisocyanate comprising reacting a diamine and phosgene at a temperature above the boiling point of the diamine within a mean contact time of from 0.5 to 5 seconds with a mean deviation in the contact time of no more than 6%. 
     
     
       2. The process of claim 1 in which the diamine and phosgene are heated separately to a temperature of from about 200° to about 600° C. and mixed continuously in a static mixing device within a period of from 0.1 to 0.3 seconds. 
     
     
       3. The process of claim 2 in which the mixture is mixed until a degree of separation of at least 10 -  3 is achieved. 
     
     
       4. The process of claim 3 in which the diamine in vaporous form is diluted with an inert gas or with vapors of an inert solvent. 
     
     
       5. The process of claim 2 in which the mixture leaving the mixing device is conveyed continuously through a cylindrical reaction chamber maintained at a temperature of 200° to 600° C. in a manner such that the flow has a Reynolds number of more than 4000 or a Bodenstein number of more than 100. 
     
     
       6. The process of claim 5 in which the mixture is present in the cylindrical reaction chamber until the reaction is completed. 
     
     
       7. The process of claim 5 in which the mixture leaving the reaction chamber in the form of a gas is cooled at a temperature such that the diisocyanate is condensed but any carbamic chloride of the diamine will be decomposed. 
     
     
       8. The process of claim 7 in which any uncondensed diisocyanate is separated from the gas mixture by washing the gas mixture with an inert solvent. 
     
     
       9. The process of claim 8 in which the inert solvent is recovered by distillation.